We have studied the atomic structure of the CeO2(001) surface as an example
for a polar "type III" surface by scanning tunnelling microscope (STM), lo
w energy electron diffraction (LEED) and atomistic simulation. High resolut
ion STM on single crystalline CeO2(001) revealed a root2/2(3 x 2)R45 degree
s surface reconstruction. Calculation confirmed oxygen in the top layer. Up
on removal of further oxygen, Ce ions in the subsurface layer are reduced t
o Ce3+. Because oxygen from bridging positions is removed during this proce
ss the surface maintains its root2/2(3 x 2)R45 degrees reconstruction. Atom
istic modelling showed that an arrangement of Ce3+ ions in lines is energet
ically favourable compared to other structures. Among a number of surfaces
considered the root2/2(3 x 2)R45 degrees reconstruction was energetically m
ost favoured. These results confirm the experimental findings and show that
polar "type III" surfaces in metal oxides reduce their surface energy by r
econstruction.
After reoxidation and annealing a c(3 x 3) surface reconstruction was found
, LEED investigations confirmed the STM results and indicate some disorder
of the surface in the [110] direction. (C) 2001 Elsevier Science B.V. All r
ights reserved.